This invention concerns a high-speed flying shears.
The invention concerns also a method employing this flying shears to shear the leading and trailing ends of a rolled bar, as set forth in the relative main claim.
The flying shears according to the invention acts on rolled stock, whether the rolled stock be a wire rod, or a section to be supplied in bars leaving the last rolling mill stand of a rolling train.
The flying shears according to the invention is suitable to shear rolled stock travelling at even more than 120 meters per second.
It is known that the leading and trailing ends of the rolled stock leaving the last rolling mill stand of a rolling train include along their length geometric deformations, non-homogeneous structures or unacceptable inclusions and therefore have to be removed; this removal is carried out generally in the line with a flying shears.
The state of the art contains various disclosures of high-speed flying shears for rolled stock.
Embodiments which are substantially efficient but have been found unsatisfactory for rolled stock travelling at very high speeds are disclosed in FR-666.433, DE-804.056, GB-2,075,899 and FR-1.578.587.
To be more exact, these disclosed embodiments are not able to meet the required accuracy of shearing nor the required high speed.
Moreover, these embodiments entail the problem of discharging, shearing for scrap and recovering the end segments sheared by the flying shears.
Theses embodiments also involve the problems of energy consumption and the obtaining of samples.
FR-A-666.433, for instance, discloses a flying shears governed by a rolling assembly that shears the rolled stock to size with rotating blades. According to this document the rolled stock is momentarily switched along a loop so that the shearing can be performed. Even if the disclosed drive and control system is used, the invention disclosed in this document, owing to the formation of the loop, is only suitable to process rolled stock travelling at medium speeds. Moreover, no mention is made of the problem of shearing for scrap the sheared leading and trailing end segments or of obtaining sample segments.
U.S. Pat. No. 3,834,260, U.S. Pat. No. 5,040,440 and DE-A-2.900.013 disclose a flying shears employed to shear the leading and trailing ends of bars leaving a rolling train but do not describe a cycle to shear for scrap the leading and trailing end segments of the bar nor a strictly and accurately guided path of the bar downstream of the shearing area for delivery of the bar to the coiling step.
Moreover, these documents open the shears in the steps preceding and following the shearing of the leading and trailing ends; the bar is directed along a fixed and substantially straight path during the whole working cycle. This entails a very heavy load of power absorbed and dispersed by the actuation and braking means of these shears since it is necessary to bring these shears in a very short time to a very high peripheral speed substantially coinciding advantageously with the speed of feed of the bar. In the same very short time it is necessary to brake the shears, when shearing has taken place, so as to prevent the shears coming into contact again with the bar passing through.
Furthermore, this solution involves great operational difficulties in making the shears act on the bar at the exact required moment and with the necessary accuracy. In fact, extreme accuracy of shearing is achieved only by obtaining a very strict correlation between the feed of the rolled material about to have its leading and trailing ends cropped and the circumferential position of the rotating blades. All these operating problems prevent the use of the shears disclosed in these documents when the speeds of feed of the bar are greater than 60 to 80 meters per second. Besides, these documents do not teach the obtaining of sample segments.
DE-A-3.027.978 discloses a guide element which can be displaced in relation to the shearing zone so as to convey the bar lengthwise in coincidence with the blades only at the shearing moment. However, this document provides a very limited movement of this guide element and entails also in this case sharp accelerations and decelerations in a very short time if it is desired to obtain a substantial coincidence of the speed of feed of the bar with the peripheral speed of the blades.
Moreover, the movement of the guide element after the shearing of the leading end of the bar includes the return of that element to its starting position and involves of necessity the opening of the blades to prevent contact between the blades and the bar passing through.
This situation entails further structural and working complexity which prevents the device disclosed in this document from being able to be used with the high speeds required in the present production technology.
IT-A-1.214.194 in the name of the present applicants discloses a high-speed flying shears having contrarotating blades and cooperating upstream with a switch of a start-stop type. This switch is suitable to convey the rolled stock lengthwise and to be displaced laterally so as to make the rolled stock pass into the shearing area between the contrarotating blades only at the shearing moment.
The circumferential position of the contrarotating blades can be linked to the lateral position of the switch so as to determine exactly the moment when the rolled stock lies between the blades, this moment coinciding with the best shearing position of the blades themselves.
The speed of lateral displacement too of the switch is correlated functionally with the peripheral speed of the contrarotating blades, so that there is a substantial coincidence of these speeds at the shearing moment. The blade-holder drums are brought to the required peripheral speed and are then braked, when shearing has taken place, in a progressive manner in view of the fact that the bar does not pass through the shearing area before and after performance of the shearing of the leading and trailing ends. Furthermore, this document does not teach the obtaining of sample segments.
This embodiment, whilst satisfactory in itself, entails the drawback that the rolled stock leaving the shearing step is difficult to guide correctly towards the downstream stations, and this drawback involves vibrations and inaccuracies in the directing of the rolled stock towards the respective channels.
Moreover, this embodiment does not provide any natural guiding for the intake of the material downstream of the shearing assembly, whether that material consists of a bar deprived of its leading and trailing ends and directed towards a coil-forming headstock or consists of the sheared segments directed towards the scrap-shears.
The present applicants have also disclosed in document EP-A-0618033 a flying shears cooperating downstream with coiling and scrap-shearing stations; in this shears the directing of the material towards the respective stations is carried out with a two-channel switch positioned immediately downstream of the shearing assembly.
The inclusion of a specific scrap-shearing station downstream of the shears and the complexity of embodying and operating the two-channel switch so as to ensure correct directing of the material without any risks of jamming or impacts makes the flying shears disclosed in this document rather expensive.